1. Field of the Invention
The present invention relates to a driving device and related output enable signal transformation device in a liquid crystal display (LCD) device, and more particularly, to a driving device and related output enable signal transformation device for enhancing the brightness of the LCD device.
2. Description of the Prior Art
The advantages of a liquid crystal display (LCD) include lighter weight, less electrical consumption, and less radiation contamination. LCD monitors have been widely applied to various portable information products, such as notebooks, mobile phones, PDAs (Personal Digital Assistants), etc. In an LCD monitor, incident light produces different polarization or refraction effects when the alignment of liquid crystal molecules is altered. The transmission of the incident light is affected by the liquid crystal molecules, and thus magnitude of the light emitted from the liquid crystal molecules varies. The LCD monitor utilizes the characteristics of the liquid crystal molecules to control the corresponding light transmittance and produces gorgeous images according to different magnitudes of red, blue, and green light.
Please refer to FIG. 1. FIG. 1 is a block diagram of an LCD device 10 according to the prior art. The LCD device 10 includes a panel 100, a timing generator 102, a data-line-signal output circuit 104 and a scan-line-signal output circuit 106. The data-line-signal output circuit 104 includes source drivers 140 in series. The scan-line-signal output circuit 106 includes gate drivers 160 in series. FIG. 1 illustrates 3 gate drivers 160 named G0, G1 and G2 as an example, but is not limited to this number.
The operation of the LCD device 10 is described as follows. The timing generator 102 generates a data signal DATA, a horizontal synchronization signal STH and a horizontal clock signal CLK and related control signals and outputs these signals to the data-line-signal output circuit 104. On the other hand, the timing generator 102 generates a vertical synchronization signal STV, a vertical clock signal CPV and an output enable signal OE and outputs these signals to the scan-line-signal output circuit 106. The source drivers 140 in series in the data-line-signal output circuit 104 sequentially transmit the horizontal synchronization signal STH and the gate drivers 160 in series in the scan-line-signal output circuit 106 sequentially transmit the vertical synchronization signal STV. As shown in FIG. 1, the data signal DATA is transformed to the voltage signals via the data-line-signal output circuit 104 and the scan-line-signal output circuit 106 for controlling the voltage difference on the equivalent capacitor of each pixel on the panel 100 for displaying, and the data signal DATA is displayed in the following sequence: pn(x,y), pn(x+1,y), pn(x+2,y) . . . pn(x,y+1), pn(x+1,y+1), pn(x+2,y+1) . . . and so on. In addition, the output enable signal OE is utilized for performing logic operations for generating the channel output signals of the gate drivers 160, so as to adjust the efficiency of the LCD device 10. Note that, only one channel is allowed to output in a gate driver 160 at the same time.
Please refer to FIG. 2, which illustrates a block diagram of a gate driver 160 in the LCD device 10. The gate driver 160 comprises a first level shifter 200, a shift register module 202, a logic circuit 204, a second level shifter 206, a buffer 208, and a third level shifter 210. The first level shifter 200 is coupled to the timing generator 102 and is utilized for level-shifting the vertical synchronization signal STV, the vertical clock signal CPV and the output enable signal OE and outputs these signals to the shift register module 202. The shift register module 202 is coupled to the first level shifter 200 and is utilized for outputting a plurality of scan signals XO to the logic circuit 204. As shown in FIG. 2, the gate driver 160 includes k channels so that the plurality of scan signals XO are named XO(0)-XO(k−1). The logic circuit 204 is coupled to the shift register module 202 and is utilized for performing logic operations on the scan signals XO(0)-XO(k−1) and output enable signal OE for generating channel output signals. The second level shifter 206 is utilized for level-shifting the channel output signals, and the buffer 208 is utilized for buffering and outputting the channel output signals. In addition, the third level shifter 210 is utilized for level-shifting the vertical synchronization signal STV and outputting the vertical synchronization signal STV to a next gate driver 160.
Please refer to FIG. 3, which illustrates a timing diagram of a frame period of a channel output signal in the LCD device 10. As shown in FIG. 3, the LCD device 10 includes total of m channels controlled by 3 gate drivers 160, G0, G1 and G2. The shift register module 202 outputs the scan signals XO sequentially. Note that, only one channel of a gate driver 160 is allowed to output (XO is in a HIGH state) and at the same time, other channels of the same gate driver 160 are not allowed to output (XO is in a LOW state.) In addition, please refer to FIG. 4, which illustrates a timing diagram of the output enable signal OE in the LCD device 10. OE0, OE1 and OE2 respectively represent the output enable signals corresponding to the gate drivers G0, G1 and G2. The void section shown in FIG. 4 represents a data valid period of the output enable signal OE corresponding to a frame. TV—TOTAL represents a frame period, TV—ACTIVE represents a data valid period and TV—BLANK represents a blanking period. As shown in FIG. 4, because the LCD device 10 has only an output enable signal OE, the timing of OE0, OE1 and OE2 are the same. From the above, the LCD device 10 cannot drive any two channels that are not adjacent.
Generally, a motion blur frequently occurs when the LCD device displays motion pictures. In the prior art, different kinds of impulse driving methods are used to improve the blur problem. For example, a time-division driving method for a gate driver which saves a lot of frame buffers and is easily operated with the black insertion, can improve the blur problem and enhance the brightness of the LCD device. The time-division driving method means that the LCD device has to be able to drive any two channels that are not adjacent. However, the time-division driving method cannot be implemented in the LCD device 10 which has only one output enable signal OE and cannot drive any two channels that are not adjacent.
Please refer to FIG. 5. FIG. 5 is a block diagram of an LCD device 50 according to the prior art. FIG. 5 illustrates 3 gate drivers 560 named G0, G1 and G2 as an example. The LCD device 50 is similar to the LCD device 10 and the difference is that the gate drivers G0, G1 and G2 in the LCD device 50 are respectively controlled by different output enable signals OE0, OE2 and OE2. Compared with the LCD device 10, each gate driver 560 is controlled by a dedicated output enable signal that is different from each other, so that the time-division driving method can be implemented in the LCD device 50.
Please refer to FIG. 6. FIG. 6 is a timing diagram of a vertical synchronization signal STV and three different output enable signals OE0, OE2 and OE2 in the LCD device 50. Note that, one (or more) additional impulse signal STV2, which is used for inserting a black frame between two normal frames, is inserted between two sequential vertical synchronization signals STV. In addition, the void section OED shown in FIG. 6 represents a data valid period of the output enable signal OE0/OE1/OE2 corresponding to a normal frame, and the dotted section OEB shown in FIG. 6 represents a period of the output enable signal OE0/OE1/OE2 corresponding to a black frame. TV—TOTAL represents a frame period and TK—LINE represents a period for k scan lines. From the above, the vertical synchronization signal STV is located at the coverage of OED and the impulse signal STV2 is located at the coverage of OEB. As mentioned previously, only one channel of a gate driver is allowed to output and other channels of the same gate driver are not allowed to output, so that there is an available region for the impulse signal STV2. For example, if a gate driver 560 in the LCD device 50 includes k channels, the impulse signal STV2 cannot be located in the period for k scan lines, TK—LINE. As a result, the impulse signal STV2 available region is limited by a boundary shown as the dash line in FIG. 6. The available region limits the flexibility of the impulse signal STV2. That is, the flexibility of black insertion is limited.
As shown in FIG. 6, in the LCD device 50, the smallest ratio of impulse signal available region to a frame period is TK—LINE/TV—TOTAL and the largest ratio of impulse signal available region to a frame period is (TV—TOTAL−TK—LINE)/TV—TOTAL. When the integration of the gate driver 560 is getting higher, the gate driver 560 can control more channels so that the number of gate drivers in the LCD device 50 is reduced and the number of output enable signals is reduced, so that the flexibility of time-division driving method is limited. Correspondingly, the flexibility of black insertion is limited and the brightness of the LCD device 50 is decreased.
In a word, in the prior art time-division driving method, a plurality of output enable signals are used to control gate drivers for enhancing the flexibility of black insertion for improving the blur problem when displaying motion pictures. On the other hand, with the advancement of semiconductor manufacture, the number of gate drivers required in the LCD device is reduced and correspondingly, the number of output enable signals is reduced and the impulse signal available region is limited. As a result, the flexibility of time-division driving method is limited and the brightness of the LCD device is decreased.